1. Field of the Invention
The present invention relates to a method of manufacturing a nitride semiconductor light-emitting device, and more specifically to a method of manufacturing a nitride semiconductor light-emitting device having an active layer with improved crystal quality and having high light-emitting efficiency.
2. Description of the Background Art
Generally, the active layer of the nitride semiconductor light-emitting device has a multiple quantum well structure in which an Inx1Ga1-x1N well layer and an Inx2Ga1-x2N barrier layer (x1>0, x2≧0, x1>x2) having different bandgaps from each other are alternately stacked (for example, Japanese Patent Laying-Open No. 06-268257). The multiple quantum well structure is used to allow a light-emitting layer to be formed with a thin well layer having a thickness of about 2-5 nm while ensuring the state density of the carrier contributing to light emission. Thus, it becomes possible to provide a light-emitting device having higher light-emitting efficiency than in the case where the bulk of the InGaN layer is used as an active layer.
However, in the case where the active layer has a multiple quantum well structure, the well layer and the barrier layer are different in In composition ratio and therefore different in surface energy, which makes it difficult to provide steep interfaces between the well layer and the barrier layer and between the barrier layer and the well layer. In this interface that is not steep, the well layer as a light-emitting layer has a spatially nonuniform thickness. Generally, the quantum efficiency greatly depends on the thickness of the well layer. Accordingly, the well layer having a nonuniform thickness produces a portion having low quantum efficiency, which causes the overall light-emitting efficiency of the light-emitting device to be decreased.
Japanese Patent Laying-Open No. 2000-261106 discloses that Si is doped as an impurity during the crystal growth of the multiple quantum well layer for the purpose of improving the light-emitting efficiency. However, this method poses a problem that the crystal quality deteriorates due to the doping of the impurity during the crystal growth.
Furthermore, Japanese Patent Laying-Open No. 09-214052 discloses that the growth of the AlGaAs active layer is interrupted before or during the growth thereof to add a small amount of indium (In) to the crystal surface. However, in this case, the active layer does not contain In, which causes dispersion and incorporation of In into the crystal, with the result that the device may be affected. In addition, the amount of In to be added must be precisely controlled such that the amount is less than 5 atom percent relative to the Al composition of the active layer, and the supply amount of In is restricted.